1. Field of the Invention
This invention relates to optical lenses for correcting vision defects and more particularly to an "anchored" contact lens for correction of presbyopia and other vision defects.
2. Description of the Prior Art
Prior art attempts to provide contact lenses for the correction of presbyopia have not been particularly successful. In presbyopic patients, the lens providing the "reading" or near vision correction must have positional stability relative to the lower eyelid, so that it will cover the pupil of the eye only when the eyeball is rotated downwardly to assume a reading position but will not cover the pupil when the eye assumes a straight ahead or distance vision position for which either no correction or only a distance correction is required.
The older type of contact lens, the so-called "scleral lens", provided a high degree of positional stability because it was supported and positioned by the scleral portion of the eyeball and was permitted little rotational or translational movement relative to the eye socket and lower eyelid. However, the inherent design of this lens presented many clinical difficulties during the fitting and wearing of the lens which eventually led to the development of the so-called "corneal lens" which essentially "floated" on the cornea of the eyeball. Although the corneal lens overcame many of the clinical problems associated with the scleral lens, it was not amenable to providing reading correction for presbyopic patients because of its floating or movable position on the cornea of the eye.
One attempt to provide reading or near vision correction in corneal lenses involved the use of a substantially circular lens in which the reading correction was provided by an annular portion which was concentrically disposed about a centrally located distance vision correction portion. This type of lens provided reading correction when the eyeball was rotated to a reading position in which the pupil was covered by the annular reading correction portion of the lens and permitted distance correction when the eyeball was rotated to a straight ahead position so that the central distance vision correction portion only covered the pupil. This arrangement was subject to many difficulties, however, because the lens was easily moved out of position on the cornea during the normal blinking action of the upper eyelid. The resulting translational or up and down movement of the lens obviously did not permit the positional stability required for satisfactory operation of the lens. Furthermore, the variously sized optic zones of these lenses produced "ghost" images, blurry vision and other defects.
Another prior art attempt to deal with presbyopia by means of corneal lenses involved the use of segmented lenses in which a distance vision correction portion or a non-vision correcting portion was arranged to cover the pupil with the eye in a straight ahead position. This lens had a reading vision correction portion which depended from the distance vision portion and which covered the pupil when the eye was rotated to a reading position. In this type of lens, problems were caused by both rotational and translational movements of the lens because of the segmental shape of the lens which required exact positional alignment for correct operation. In order to prevent rotation and translation of the lens relative to the cornea, this type of lens was provided with an outwardly or anteriorly projecting flange which engaged the margin of the lower eyelid to limit rotational movement and provide some degree of stability during blinking or other translational movements. The lens, however, still floated on the cornea and was not positionally stable. Other arrangements for preventing rotational movement of these lenses involved the use of a ballasted or weighted lens in which the heaviest and/or largest portion of the lens was disposed inferiorly of the distance correction portion so that the force of gravity tended to center the lens and prevent rotation. Unfortunately, all of these arrangements did not provide a satisfactory solution to the problem because of the wide range of lens movements which were still possible.
Still another attempt to provide presbyopic correction involved the use of a small non-contact lens having a reading correction which was cemented to the margin of the lower eyelid. This lens projected up from the lower eyelid margin and was spaced a distance from the eyeball so that when the eye was closed, the margin of the upper eyelid could pass between the lens and the eyeball to thereby permit the eye to be closed with the lens in position. Obviously, this type of lens was not a contact lens and provided some inconvenience to the wearer because of the necessity of adhesively mounting it on the margin of the lower eyelid.